This project continues the development and support of ERPLAB Toolbox, a Matlab-based open source software package for the analysis of event-related potential (ERP) data. ERPs provide information about brain activity related to perception, cognition, emotion, and action with millisecond resolution and are widely used to study a broad range of basic and translational science issues in psychology, neuroscience, psychiatry, neurology, and related fields. There has been an explosion in ERP research, but progress has been hampered by the limited abilities of commercial ERP analysis software and the lack of full-featured open source ERP analysis packages. This situation has slowed the development of new directions in ERP research, instead encouraging researchers to continue with existing approaches supported by the built-in functions of the available commercial analysis packages. ERPLAB Toolbox directly addresses these problems. It adds all the main ERP processing routines to an open source EEG processing package, EEGLAB. ERPLAB builds on EEGLAB by adding powerful tools for the subsequent stages of ERP analysis. All ERPLAB tools can be accessed from the GUI, and they can also be accessed from Matlab scripts to provide automation and customization. ERPLAB provides powerful but easy-to-use tools for the basic and advanced analysis procedures that are commonly used by ERP researchers. In addition, ERPLAB can be easily extended by anyone with rudimentary programming skills, making it possible for researchers to create innovative new data processing and analysis procedures and link ERPs with other types of biological data. ERPLAB has been publicly available for 4 years, and in that time it has been downloaded over 10,000 times and has been cited in 165 publications (a number that is increasing exponentially). It has been used to replace expensive commercial software for conventional analyses, and it has been used as a platform for developing new analysis procedures and for linking ERP data with other open source toolboxes. In the proposed funding period, we will continue to provide basic support and develop new features that reflect trends in basic, translational, and clinical research. We will focus on four themes: increased workflow efficiency; new tools for single-trial analyses; advanced statistical tools; and additional documentation and examples. Our goal is to give researchers free, open-source tools that allow them to conduct innovative, state-of-the-art, high-impact research on normal and disordered brain function.